Conventionally, as automatic focusing (AF) technologies in image pickup apparatus such as cameras and video cameras, various proposals have been made. For example, there is proposed phase difference autofocus using a through the lens (TTL) method in which a separating unit is provided in an optical path in an imaging optical system, and a focusing state is detected using a separated beam to perform autofocus control. In addition, there is also proposed external ranging autofocus using a non-TTL method in which a beam which does not enter nor pass through the imaging optical system is used. Further, there is proposed image autofocus using so-called hill climbing method in which an image signal output from an image pickup element is used to compute a focus evaluating value. Further, there is proposed a hybrid autofocus system in which the image autofocus is combined with the phase difference autofocus or the external ranging autofocus.
In focus detecting apparatus using the TTL method such as the phase difference autofocus or the non-TTL method such as the external ranging autofocus, a phase difference is determined by performing correlation computation using an image signal output from the focus detecting apparatus. In this case, a true focusing point is determined using a degree of coincidence between two images as a correlated evaluating value. In general, a defocus amount with respect to a focusing proposed point is determined based on a phase difference with which the correlated evaluating value takes an extreme and maximum value. However, in a case where data obtained from the focus detecting apparatus has a cyclic pattern, multiple focusing proposed points that have substantially identical correlated evaluating values are computed when focus detecting computation is performed. Consequently, it has been difficult to obtain a true focusing target position.
Patent Literature 1 proposes a method in which, when an object having a cyclic pattern is detected, a point where a contrast value of data output from a phase difference sensor takes a maximum value is assumed to be a true focusing point, and individual focusing proposed points are searched for the true focusing point. In addition, in each of the hybrid autofocus systems of Patent Literatures 2, 3 and 4, there is proposed a method involving searching for the focusing point at which contrast takes a maximum value by using only the image autofocus for an object having the cyclic pattern.